1. Field of the Invention
The invention relates to a system and a method for transferring electric energy to a vehicle, in particular to a track bound vehicle such as a light rail vehicle (e.g. a tram).
2. Description of the Prior Art
In particular track bound vehicles, such as conventional rail vehicles, mono-rail vehicles, trolley busses and vehicles which are guided on a track by other means, such as other mechanical means, magnetic means, electronic means and/or optical means, require electric energy for propulsion on the track and for operating auxiliary systems, which do not produce traction of the vehicle. Such auxiliary systems are, for example, lighting systems, heating and/or air condition system, the air ventilation and passenger information systems. However, more particularly speaking, the present invention is related to transferring electric energy to a vehicle which is not necessarily (but preferably) a track bound vehicle. Generally speaking, the vehicle may be, for example, a vehicle having an electrically operated propulsion motor. The vehicle may also be a vehicle having a hybrid propulsion system, e.g. a system which can be operated by electric energy or by other energy, such as electrochemically stored energy or fuel (e.g. natural gas, gasoline or petrol).
Track bound vehicles, in particular vehicles for public passenger transport, usually comprise a current collector (alternatively a device) for mechanically and electrically contacting a line conductor along the track, such as an electric rail or an overhead line. At least one propulsion motor on board the vehicles is fed with the electrical power from the external track or line and produces mechanical propulsion force.
Trams and other local or regional trains are operated usually via overhead lines within cities. However, especially in historic parts of cities, overhead lines are undesirable. On the other hand, conductor rails in the ground or near the ground cause safety problems.
WO 95/30556 A2 describes a road way-powered electric vehicle system. The all-electric vehicle has one or more on-board energy storage elements or devices that can be rapidly charged or energized with energy obtained from an electrical source, such as a network of electromechanical batteries. The energy storage elements may be charged while the vehicle is in operation. The charging occurs through a network of power coupling elements, e.g. coils embedded in the road way.
Placing the coils at selected locations along the length of the roadway has the disadvantage that the energy storage on board the vehicle needs a large storage capacity. In addition, if the vehicle does not reach the next coil in time, the vehicle might run out of energy for propulsion or other purposes. Therefore, at least for some applications, it is preferred to transfer energy to the vehicle continuously along the path of travel, i.e. along the track.
Inductively transferring energy from the track to the vehicle, i.e. producing electromagnetic fields, is subject to restrictions regarding EMC (electromagnetic compatibility). On one hand, electromagnetic fields may interfere with other technical devices. On the other hand, people and animals should not be subjected to electromagnetic fields permanently. At least, the respective limit values for field intensity must be observed.